Explainer | Coronavirus: what does suspension of Oxford-AstraZeneca trials tell us about vaccine development?

Independent committee must investigate any possible link between participant’s unexplained illness and the trial vaccine

Thousands have received test vaccine and the company plans to enrol up to 50,000 volunteers worldwide for the last stage of trials

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Clinical trials for a Covid-19 vaccine candidate being developed by Oxford University and AstraZeneca have been suspended after a participant was found to be ill. Photo: AP

Published: 11:30am, 10 Sep 2020Updated: 12:32am, 11 Sep 2020

Oxford University and pharmaceutical giant AstraZeneca have suspended clinical trials of a potential Covid-19 vaccine pending an independent investigation after “a potentially unexplained illness” was found in a volunteer, but scientists said it was too early to tell if it was linked to the vaccine.

Jeremy Farrar, director of London-based research charity Wellcome Trust, said the investigators would have to find out if the illness was caused by the vaccine candidate, the placebo or the control vaccine used for comparison – or if it was unrelated – and the trials could be on hold for days or weeks.

“In this case, probably a few weeks, I would imagine, before it would restart again, depending on the investigation,” he told a media briefing on Wednesday.

If the illness was found to have been caused by the experimental vaccine, the investigators would then have to find out if it had to do with the adenovirus vector used in it, or the vaccine construct that was used to express the antigen, he said. The information would then be shared with other vaccine developers using similar technology, he added.

The Oxford/AstraZeneca vaccine candidate uses an adenovirus from chimpanzees as a vector to express the spike protein of the coronavirus that causes Covid-19. Johnson & Johnson, Russia’s Sputnik V vaccine candidate and Chinese pharmaceutical firm CanSino use other types of adenoviruses as vectors to express the protein.

Farrar said there had been no similar incident in trials for other adenovirus vector vaccines.